The present disclosure relates to a method for propelling a vehicle having a power-train comprising a primary power source accompanied with a primary power torque curve and a secondary power source accompanied with a secondary power torque curve, the primary power source being adapted to deliver a maximum torque output in relation to rotational speed according to said primary power torque curve and the secondary power source being adapted to deliver a maximum torque output in relation to rotational speed according to said secondary power torque curve, the vehicle being adapted to be propelled by either one of the primary power source and the secondary power source or by both together, the powertrain further comprising a powertrain limit curve which is adapted to where applicable restrict a current driver demand from a driver of the vehicle in relation to said primary power torque curve and said secondary power torque curve when propel-ling the vehicle. The present disclosure also relates to a vehicle which is adapted to perform the method.
In the automotive industry the general trend is to reduce fuel consumption end exhaust gas emissions in the vehicles, especially in commercial vehicles having internal combustion engines. This is also true however for passenger cars, busses etc. This may be achieved in many different ways. One strategy has been to reduce the engine size in general. However there may be times when such a downsized engine is not sufficient to deliver the required torque to propel the vehicle. This is especially true when the vehicle, such as a commercial vehicle in cargo traffic or a construction type of vehicle, is heavily loaded. In combination with a downsized engine also a secondary and further assistance motor(s) can be implemented, which is (are) adapted to assist the main engine at times when the power demand delivered by the main engine is insufficient.
One way to complement a downsized internal combustion engine may be to utilize a secondary power source in combination with an energy buffer. These vehicles that combine several power sources are referred to as hybrid vehicles. One example of a secondary power source and energy buffer is an electric machine and battery set. When a vehicle combines an internal combustion engine with an electric machine and a battery set they are referred to as hybrid electric vehicles. The battery sets are increasingly improved in efficiency, power and life time properties. The electric machine may be run both as a generator to store energy in the battery set at times when there is a surplus of energy (such as during deceleration sequences for example), and as a motor to propel the vehicle by delivering energy from the battery set to the vehicle wheels. The vehicle may be run on either one or both of the internal combustion engine and the electric machine. The internal combustion engine may be run on any type of commercially available fuel, although diesel still is the most common fuel for vehicles such as heavy trucks.
The electric machine is often designed to give good performance properties when propelling the vehicle in a purely electric mode as well as to meet demands on fuel economy, such that high brake energy regeneration is achieved. When driving the vehicle in hybrid mode, i.e. by utilising both the internal combustion engine and the electric machine, the power output from the electric machine is consequently limited. There are several reasons for running the electric machine on a limited capacity under such conditions. It is advantageous to limit the vehicle acceleration such that the vehicle behaves in a similar manner as a non-hybrid vehicle and so that the acceleration is not too powerful. It is also advantageous not to use too much electric power for saving the battery lifespan. It is also advantageous not to overheat the electric machine, which otherwise could be the case.
It is noted that hybrid vehicles also may be of other kinds. The general term hybrid vehicle is used when a vehicle combines a primary power source with a secondary power source. It also needs an energy buffer or an energy storage system. The primary power source may be any kind of internal combustion engine, such as running on diesel, petrol, dimethylether or other appropriate fuel or fuel combination. The secondary power source may be an electric machine, but also a flywheel or a hydraulic motor. The hybrid vehicle would hence be called a mechanical hybrid vehicle and a hydraulic hybrid vehicle respectively. The energy buffer or energy storage system for the electric machine may be a battery set or a super capacitor, whereas for the flywheel it is the moment of inertia which is stored in the flywheel, and for the hydraulic motor it is a pressure tank.
It is desirable to further improve the drivability of a hybrid vehicle.
According to a first aspect a method for propelling a vehicle is disclosed. The vehicle has a powertrain comprising a primary power source accompanied with a primary power torque curve and a secondary power source accompanied with a secondary power torque curve. The primary power source is adapted to deliver a maximum torque output in relation to rotational speed according to said primary power torque curve and the secondary power source is adapted to deliver a maximum torque output in relation to rotational speed according to said secondary power torque curve. The vehicle is adapted to be propelled by either one of the primary power source and the secondary power source or by both together. The powertrain further comprises a powertrain limit curve which is adapted to where applicable restrict a current driver demand from a driver of the vehicle in relation to said primary power torque curve and said secondary power torque curve when propelling the vehicle. The method comprises when propelling the vehicle by both the primary power source and the secondary power source:
determining a current driver demand,
determining a current propulsion adaption condition for the vehicle, adjusting the powertrain limit curve according to a propulsion adaption torque factor depending on said current propulsion adaption condition,                where applicable restricting said current driver demand according to said adjusted powertrain limit curve, and        
requesting the powertrain to propel the vehicle according to the thus possibly restricted current driver demand.
A method of propelling a vehicle of this kind adjusts the power that is available from the powertrain to propel the vehicle such that the propulsion of the vehicle is adjusted accordingly. Under normal propulsion conditions, the power needed to propel the vehicle may be kept at a “normal” level or at a “standard setting” in order to take fuel economy, exhaust gas emissions and to capacities for each one of the primary and secondary power sources into account. However, it may be advantageous and desirous to adjust the power that is made available to the propulsion of the vehicle through adjusting the power-train limit curve. Hereby a quick response from the vehicle to the driver's commands may be achieved, or additional power may be utilised. The opposite situation may also apply, i.e. that a slower response or less power is made available for propelling the vehicle. A more fine-tuned cooperation between the primary power source and the secondary power source may consequently be achieved. This may also improve the lifetime of any battery sets or similar additional features if such are included in the powertrain.
Determining a prevailing propulsion adaption condition is an advantageous manner in which to determine under what circumstances the vehicle travels. Hereby the propulsion of the vehicle may be adapted to the prevailing propulsion conditions, i.e. to the prevailing total power demand for the vehicle. The propulsion adaption torque factor is a function of the prevailing propulsion adaption condition. Hereby the efficiency of the propulsion of the vehicle may be balanced against the power consumption needed for the propulsion. Different prevailing propulsion conditions may consequently result in different propulsion adaption torque factors, or the adjusting of a propulsion adaption torque factor, continuously or stepwise where appropriate.
According to an embodiment the propulsion adaption torque factor is a scaling factor being a function of the prevailing propulsion adaption condition.
This is a simple manner to take the prevailing propulsion adaption conditions into account and to adjust the powertrain limit curve.
According to an embodiment the scaling factor is stepwise linear.
According to an embodiment the step of requesting the powertrain to propel the vehicle according to the thus possibly restricted current driver demand involves transforming said possibly restricted current driver demand into a powertrain torque demand.
According to an embodiment the method further comprises distributing said power-train torque demand between the primary power source and the secondary power source.
According to an embodiment the method comprises resetting the powertrain limit curve when the prevailing propulsion adaption condition is terminated.
In order to minimise e.g. the additional power consumption by the electric machine which may be into effect during a prevailing propulsion adaption condition, the powertrain limit curve may be reset as soon as e.g. a prevailing propulsion adaption condition is terminated. Thereby the powertrain capacity is used most efficiently. This behaviour may be advantageous when the propulsion adaption torque factor has a discontinuous constitution, e.g. being limited to adjust the powertrain limit curve at only certain times such as when a particular event occurs.
According to an embodiment the step of detecting a prevailing propulsion adaption condition for the vehicle comprises detecting any one or a combination of the following: detecting that the vehicle is located in or at a slope, detecting a loading situation of the vehicle, and detecting that the vehicle is being ahead of or belated in relation to a desired schedule.
These conditions may require additional power to propel the vehicle and it is hence advantageous to detect if any of them prevail, either alone or in combination. The detection may be performed continuously during using of the vehicle. This means that it can be made both when the vehicle is propelled and at a standstill. It may also be made when both the primary power source and the secondary power source are briefly “shut off since that may occur at a standstill if the vehicle is provided with a start/stop functionality. A typical situation of that kind is a bus in commercial traffic which stops at a bus stop for letting travellers on and off, or when a vehicle stops at a traffic signal.
According to an embodiment the step of detecting that the vehicle is located in or at a slope involves using inclination detecting means and detecting if the inclination sens-ing means detect an upward or downward slope being equal to or greater than a predetermined inclination value.
Such inclination detecting means may include an inclination sensor located in the vehicle, a vehicle navigation system such as a Global Positioning System (GPS) system having access also to information of altitudes, or a vehicle navigation system such as a GPS system, which is adapted to record the altitude of a position if the vehicle passes said location in order to use the altitude information the next time the same location is passed.
According to an embodiment said predetermined inclination value corresponds to an upward slope of at least 7.5%, preferably of at least 10%, and more preferably of at least 12.5%.
According to an embodiment the step of detecting a loading situation of the vehicle involves using weight sensing means and detecting that the weight sensing means detect a payload in the vehicle being equal or greater than a predetermined weight value.
Such weight sensing means may include gauges of different kinds located in or at a vehicle suspension system, such that the additional payload on the suspension system may be estimated in relation to the vehicle dead weight.
According to an embodiment said predetermined weight value corresponds to a payload of 30%, preferably of 50%, and more preferably of 70% in relation to a vehicle dead weight.
According to a second aspect a vehicle is disclosed which has a powertrain comprising a primary power source accompanied with a primary power torque curve and a secondary power source accompanied with a secondary power torque curve. The primary power source is adapted to deliver a maximum torque output in relation to rotational speed according to said primary power torque curve and the secondary power source is adapted to deliver a maximum torque output in relation to rotational speed according to said secondary power torque curve. The vehicle is adapted to be propelled by either one of the primary power source and the secondary power source or by both together. The powertrain further comprises a powertrain limit curve which is adapted to where applicable restrict a current driver demand from a driver of the vehicle in relation to said primary power torque curve and said secondary power torque curve when propelling the vehicle. The vehicle is further adapted to perform the method as disclosed above. A vehicle of this kind is associated with corresponding advantages as are disclosed in relation to the method according to the first aspect.
According to an embodiment the primary power source is an internal combustion engine.
According to an embodiment the secondary power source is an electric machine.